Subcritical reactors(SCRs)or subcritical assemblies(SCAs)are the main infrastructure for designing power reactors.These reactors are widely used for training and research because of their high level of inherent safety...Subcritical reactors(SCRs)or subcritical assemblies(SCAs)are the main infrastructure for designing power reactors.These reactors are widely used for training and research because of their high level of inherent safety.The objective of this study is to design a subcritical reactor using a pressurized water reactor(PWR)conventional fuel following two safety points.In the first approach,deeply placed SCR cores with an infinite multiplication factor(k_(∞))of less than unity were identified using the DRAGON lattice code.In the second approach,subcritical reactor cores with an effective multiplication factor(k_(eff))of less than unity were determined by coupling the cell calculations of the DRAGON lattice code and core calculations of the DONJON code.For the deeply subcritical reactor design,it was found that the reactor would remain inherently subcritical while using fuel rods with ^(235)U enrichment of up to 0.9%,regardless of the pitch of the fuel rods.In the second approach,the optimal pitches(1.3 to 2.3 cm)were determined for different fuel enrichment values from 1 to 5%.Subsequently,the k_(eff) was obtained for a fuel rod arrangement of 8×8 to 80×80,and the states in which the reactor would be subcritical were determined for different fuel enrichments at the corresponding optimal pitch.To validate the models used in the DRAGON and DONJON codes,the k_(eff) of the Isfahan Light Water Subcritical Reactor(LWSCR)was experimentally measured and compared with the results of the calculations.Finally,the effects of fuel and moderator temperature changes were investigated to ensure that the designed assemblies remained in the subcritical state at all operational temperatures.展开更多
Subcritical crack growth(SCG)in fluid-rock interactions plays a crucial role in understanding crustal deformation and fracture network development.Using a double-torsion technique,the subcritical crack growth and frac...Subcritical crack growth(SCG)in fluid-rock interactions plays a crucial role in understanding crustal deformation and fracture network development.Using a double-torsion technique,the subcritical crack growth and fracture characteristics of Zhangzhou granite were investigated under fluids with different pH values.Subcritical crack growth index(SCI)was reduced in both acidic and alkaline fluids compared with the neutral environment,with reduction percentages of 9.8%e31.9%under acidic environment(pH=1-5)and 8.3%e17.5%under alkaline environment(pH=10-14),respectively.In contrast,the weakening effect of fluid pH values on critical stress intensity was less than that of SCI.Scanning electron microscopy(SEM)results showed that grain boundaries were prone to dissolution compared to the basal surface,proving that subcritical cracks preferentially propagate along the grain boundaries.Fracture toughness was insensitive to fluid pH values in the short term but sensitive to solution salinity.Considering mineral compositions and contents,a rock dissolution rate was defined,and a SCI prediction model was proposed,which was demonstrated to be capable of estimating variations in SCI under various fluid environments for different rock types and could provide valuable insights for engineering applications and environmental assessments.展开更多
Two experimental X80 steels with different Cr contents(0.13,0.40 wt.%)were designed to study the influence of Cr content on the microstructure transformation and properties in the coarse-grained heat-affected zone by ...Two experimental X80 steels with different Cr contents(0.13,0.40 wt.%)were designed to study the influence of Cr content on the microstructure transformation and properties in the coarse-grained heat-affected zone by using a Formastor-F II thermal dilatometer and to simulate the microstructure of the subcritically reheated coarse-grained heat-affected zone(SCGHAZ)by means of the Gleeble-3500 thermal simulator,along with the scanning electron microscope,transmission electron microscope,and electron backscattering diffraction test methods to characterize the microstructures at 650℃.The findings indicate that a higher Cr content can promote the formation of bainitic ferrite(BF),while the microhardness and impact toughness of SCGHAZ are improved.Granular bainite and BF dominated the microstructures formed by the two experimental steels at 650℃,respectively.For experimental steels mainly composed of BF,they have a high proportion of high-angle grain boundaries(HAGB),and the misorientation angle of HAGB is mostly greater than 55°.Moreover,the distribution of martensite-austenite(M-A)constituents in SCGHAZ altered from dense to sparse,and the form altered from elongated to island-like when the Cr concentration was changed from 0.13 to 0.40 wt.%.Consequently,by suitably increasing the concentration of Cr,it is possible to raise the density of HAGB and improve the shape of M-A constituents,allowing SCGHAZ to have a higher toughness.展开更多
This study examines the nonlinear behaviors of a clamped-clamped porous pipe made of a functionally graded material(FGM)that conveys fluids and is equipped with a retaining clip,focusing on primary resonance and subcr...This study examines the nonlinear behaviors of a clamped-clamped porous pipe made of a functionally graded material(FGM)that conveys fluids and is equipped with a retaining clip,focusing on primary resonance and subcritical dynamics.The nonlinear governing equations for the FGM pipe are derived by the extended Hamilton's principle,and subsequently discretized through the application of the Galerkin method.The direct method of multi-scales is then used to solve the derived equations.A thorough analysis of various parameters,including the clip stiffness,the power-law index,the porosity,and the clip location,is conducted to gain a comprehensive understanding of the system's nonlinear dynamics.Through the analysis of the first natural frequency,the study highlights the influence of the flow velocity and the clip stiffness,while the comparisons with metallic pipes emphasize the role of FGM composition.The examination of the forced response curves reveals saddle-node bifurcations and their dependence on parameters such as the detuning parameter and the power-law index,offering valuable insights into the system's nonlinear resonant behavior.Furthermore,the frequency-response curves illustrate the hardening nonlinearities influenced by factors such as the porosity and the clip stiffness,revealing nuanced effects on the system response and resonance characteristics.This comprehensive analysis enhances the understanding of nonlinear behaviors in FGM porous pipes with a retaining clip,providing key insights for practical engineering applications in system design and optimization.展开更多
High-level waste is an important safety issue in the development of nuclear power.A proposed solution is the transmutation of waste in fast reactors.The exclusion of the risk of supercriticality by using subcritical r...High-level waste is an important safety issue in the development of nuclear power.A proposed solution is the transmutation of waste in fast reactors.The exclusion of the risk of supercriticality by using subcritical reactors is currently under development.Controlling the subcriticality level in such reactors presents difficulties.A problem is posed by the so-called space effect observed when using in reactors many neutron detectors in different locations of the core and reflector.Reactivity obtained from measure-ments,for example,by the Sjo¨strand method,differs by nonnegligible values.Numerical corrections can partially improve this situation.The use of a monoisotopic fission chamber set,designed for a given reactor,when each chamber is intended for a specific position in the system,can improve the situation.A question arises about the sensitivity of the results to reactivity changes.This issue is analyzed by computer simulation for possible fissionable and fissile nuclides for the total range of control rod insertion,changes in reactor fuel enrichment,and fuel temperature.The tested sensitivity was satisfactory at most levels from several dozen to several hundred pcm.A case study was conducted using the VENUS-F core model.展开更多
The hydrolysis technology and reaction kinetics for amino acids production from fish proteins in subcritical water reactor without catalysts were investigated in a reactor with volume of 400 ml under the conditions of...The hydrolysis technology and reaction kinetics for amino acids production from fish proteins in subcritical water reactor without catalysts were investigated in a reactor with volume of 400 ml under the conditions of reaction temperature from 180-320℃, pressure from 5-26 MPa, and time from 5-60 rain. The quality and quantity of amino acids in hydrolysate were determined by bioLiquid chromatography, and 17 kinds of amino acids were obtained. For the important 8 amino acids, the experiments were conducted to examine the effects of reaction temperature, pressure and time on amino acids yield. The optimum conditions for high yield are obtained from the experimental results. It is found that the nitrogen and carbon dioxide atmosphere should be used for leucine, isoleucine and histidine production while the air atmosphere might be used for other amino acids. The reaction time of 30 rain and the experimental temperature of 220℃, 240℃ and 260℃ were adopted for reaction kinetic research. The total yield of amino acids versus reaction time have been examined experimentally. According to these experimental data and under the condition of water excess, the macroscopic reaction kinetic equation of fish proteins hydrolysis was obtained with the hydrolysis reaction order of 1.615 and the rate constants being 0.0017, 0.0045 and 0.0097 at 220℃, 240℃ and 260℃ respectively. The activation energy is 145.1 kJ·mol^- 1.展开更多
Effect of cryogenic treatment on the microstructure, hardening behavior and abrasion resistance of 14Cr2Mn2V high chromium cast iron （HCCI） subjected to subcritical treatment was investigated. The results show that ...Effect of cryogenic treatment on the microstructure, hardening behavior and abrasion resistance of 14Cr2Mn2V high chromium cast iron （HCCI） subjected to subcritical treatment was investigated. The results show that cryogenic treatment after subcritical treatment can obviously improve the hardness and abrasion resistance of HCCI because abundant retained austenite is transformed into martensite and fine secondary carbides E（Fe, Cr）23 C6 ] precipitate. The amount of martensite and precipitated secondary carbide in HCCI experiencing subcritical treatment followed by cryogenic treatment was more than that experiencing the subcritical treatment followed by air cooling. When the abrasion resistance of HCCI reaches the maximum, its microstructure contains about 15 % retained austenite. Cryogenic treatment can further reduce the austenite content but the retained austenite cannot be transformed in to martensite completely.展开更多
The subcritical crack growth and fracture toughness in peridotite, lherzolite and amphibolite were investigated with double torsion test. The results show that water-rock interaction has a significant influence on sub...The subcritical crack growth and fracture toughness in peridotite, lherzolite and amphibolite were investigated with double torsion test. The results show that water-rock interaction has a significant influence on subcritical crack growth. With water-rock interaction, the crack velocity increases, while the stress intensity factor declines, which illustrates that water-rock interaction can decrease the strength of rocks and accelerate the subcritical crack growth. Based on Charlse theory and Hilling & Charlse theory, the test data were analyzed by regression and the correlation coefficients were all higher than 0.7, which shows the correlation is significant. This illustrates that both theories can explain the results of tests very well. Therefore, it is believed that the subcritical crack growth attributes to the breaking of chemical bond, which is caused by the combined effect of the tensile stress and the chemical reaction between the material at crack tip and the corrosive agent. Meanwhile, water-rock interaction has a vital effect on fracture toughness. The fracture toughness of samples under atmospheric environment is higher than that of samples immersed in water. And water-rock interaction has larger influence on fracture toughness in amphibolite than that in peridotite and lherzolite.展开更多
In 2011,the Chinese Academy of Sciences launched an engineering project to develop an acceleratordriven subcritical system(ADS)for nuclear waste transmutation.The China Lead-based Reactor(CLEAR),proposed by the Instit...In 2011,the Chinese Academy of Sciences launched an engineering project to develop an acceleratordriven subcritical system(ADS)for nuclear waste transmutation.The China Lead-based Reactor(CLEAR),proposed by the Institute of Nuclear Energy Safety Technology,was selected as the reference reactor for ADS development,as well as for the technology development of the Generation IV lead-cooled fast reactor.The conceptual design of CLEAR-I with 10 MW thermal power has been completed.KYLIN series lead-bismuth eutectic experimental loops have been constructed to investigate the technologies of the coolant,key components,structural materials,fuel assembly,operation,and control.In order to validate and test the key components and integrated operating technology of the lead-based reactor,the lead alloy-cooled non-nuclear reactor CLEAR-S,the lead-based zero-power nuclear reactor CLEAR-0,and the lead-based virtual reactor CLEAR-V are under realization.展开更多
The accelerator-driven subcritical system (ADS) with a hard neutron energy spectrum was used to study transmutation of minor actinides (MAs). The aim of the study was to improve the efficiency of MA transmutation whil...The accelerator-driven subcritical system (ADS) with a hard neutron energy spectrum was used to study transmutation of minor actinides (MAs). The aim of the study was to improve the efficiency of MA transmutation while ensuring that variations in the effective multiplication factor (keff) remained within safe margins during reactor operation. All calculations were completed using code COUPLE3.0. The subcritical reactor was operated at a thermal power level of 800 MW, and a mixture of mononitrides of MAs and plutonium (Pu) was used as fuel. Zirconium nitride (ZrN) was used as an inert matrix in the fuel elements. The initial mass composition in terms of weight percentages in the heavy metal component (IHM) was 30.6% Pu/IHM and 69.4% MA/IHM. To verify the feasibility of this MA loading scheme, variations in keff, the amplification factor of the core, maximum power density and the content of MAs and Pu were calculated over six refueling cycles. Each cycle was of 600 days duration, and therefore, there were 3600 effective full power days. Results demonstrated that the effective transmutation support ratio of MAs was approximately 28, and the ADS was able to efficiently transmute MAs. The changes in other physical parameters were also within their normal ranges.It is concluded that the proposed MA transmutation scheme for an ADS core is reasonable.展开更多
Rock is more sensitive to tensile loading than compressive loading,since the tensile strength of rock is much lower than compressive strength.The fracture characteristics of rock in the tensile state are of great sign...Rock is more sensitive to tensile loading than compressive loading,since the tensile strength of rock is much lower than compressive strength.The fracture characteristics of rock in the tensile state are of great significance to the understanding of rock failure mechanisms.To this end,we have conducted numerical simulation researches on modeⅠcracking process of rock with varying homogeneity,using the Realistic Failure Process Analysis program.With the increase of homogeneity,cracks are concentrating to the ligament area with a decreasing number of crack bifurcations,and the main crack path is becoming smooth.Crack behaviors and mechanical properties are influenced significantly when the homogeneity index is in the range of 1.5 to 5.When the homogeneity index is greater than 30,they are not affected by rock homogeneity and the rock can be considered as essentially homogeneous.It is considered that the global and local strengths are affected by the distribution of rock mechanical properties at mesoscale,which influence the crack behaviors and mechanical characteristics.展开更多
This paper studies the local dynamics of an SDOF system with quadratic and cubic stiffness terms,and with linear delayed velocity feedback.The analysis indicates that for a sufficiently large velocity feedback gain,th...This paper studies the local dynamics of an SDOF system with quadratic and cubic stiffness terms,and with linear delayed velocity feedback.The analysis indicates that for a sufficiently large velocity feedback gain,the equilibrium of the system may undergo a number of stability switches with an increase of time delay,and then becomes unstable forever.At each critical value of time delay for which the system changes its stability,a generic Hopf bifurcation occurs and a periodic motion emerges in a one-sided neighbourhood of the critical time delay.The method of Fredholm alternative is applied to determine the bifurcating periodic motions and their stability.It stresses on the effect of the system parameters on the stable regions and the amplitudes of the bifurcating periodic solutions.展开更多
Euphausia pacific is an important source of natural astaxanthin. Studies were carried out to assess the extractability of astaxanthin from E. pacific using subcritical 1, 1, 1,2-tetrafluoroethane （R134a）. To examine...Euphausia pacific is an important source of natural astaxanthin. Studies were carried out to assess the extractability of astaxanthin from E. pacific using subcritical 1, 1, 1,2-tetrafluoroethane （R134a）. To examine the effects of multiple process variables on the extraction yield, astaxanthin was extracted under various conditions of pressure （30-150bar）, temperature （303-343 K）, time （10-50rain）, flow rate （2-10gmin-1）, moisture content （5.5%-63.61%）, and particle size （0.25-0.109mm）. The results showed that the extraction yield increased with temperature, pressure, time and flow rate, but decreased with moisture content and particle size. A maximum yield of 87.74% was obtained under conditions of 100bar, 333K, and 30min with a flow rate of 6gmin-1 and a moisture content of 5.5%. The substantial astaxanthin yield obtained under low-pressure conditions demonstrates that subcritical R134a is a good alternative to CO2 for extraction of astaxanthin from E. pacific.展开更多
An accelerator-driven subcritical system(ADS)is driven by an external spallation neutron source, which is generated from a heavy metal spallation target to maintain stable operation of the subcritical core, where the ...An accelerator-driven subcritical system(ADS)is driven by an external spallation neutron source, which is generated from a heavy metal spallation target to maintain stable operation of the subcritical core, where the energy of the spallation neutrons can reach several hundred megaelectron volts. However, the upper neutron energy limit of nuclear cross-section databases, which are widely used in critical reactor physics calculations, is generally 20 MeV.This is not suitable for simulating the transport of highenergy spallation neutrons in the ADS. We combine the Japanese JENDL-4.0/HE high-energy evaluation database and the ADS-HE and ADS 2.0 libraries from the International Atomic Energy Agency and process all the data files for nuclides with energies greater than 20 MeV. We use the continuous pointwise cross-section program NJOY2016 to generate the ACE-formatted cross-section data library IMPC-ADS at multiple temperature points. Using the IMPC-ADS library, we calculate 10 critical benchmarks of the International Criticality Safety Benchmark Evaluation Project manual, the 14-MeV fixed-source problem of the Godiva sphere, and the neutron flux of the ADS subcritical core by MCNPX. To verify the correctness of the IMPCADS, the results were compared with those calculated using the ENDF/B-VII.0 library. The results showed thatthe IMPC-ADS is reliable in effective multiplication factor and neutron flux calculations, and it can be applied to physical analysis of the ADS subcritical reactor core.展开更多
The utilization of neutrons markedly affects the medical isotope yield of a subcritical system driven by an external D-T neutron source.The general methods to improve the utilization of neutrons include moderating mul...The utilization of neutrons markedly affects the medical isotope yield of a subcritical system driven by an external D-T neutron source.The general methods to improve the utilization of neutrons include moderating multiplying,and reflecting neutrons,which ignores the use of neutrons that backscatter to the source direction.In this study,a stacked structure was formed by assembling the multiplier and the low-enriched uranium solution to enable the full use of neutrons that backscatter to the source direction and further improve the utilization of neutrons.A model based on SuperMC was used to evaluate the neutronics and safety behavior of the subcritical system,such as the neutron effective multiplication factor,neutron energy spectrum,medical isotope yield,and heat deposition.Based on the calculation results,when the intensity of the neutron source was 59×10^(13)n/s,the optimized design with a stacked structure could increase the yield of ^(99)Mo to182 Ci/day,which is approximately 16% higher than that obtained with a single-layer structure.The inlet H_(2)O coolant velocity of 1.0 m/s and initial temperature of 20℃ were also found to be sufficient to prevent boiling of the fuel solution.展开更多
The long-term stability of the roof is particularly important in designing underground rock structures.To estimate the durability of roof strata in underground excavation,a computation scheme of subcritical crack grow...The long-term stability of the roof is particularly important in designing underground rock structures.To estimate the durability of roof strata in underground excavation,a computation scheme of subcritical crack growth is proposed in this study.By adopting the proposed method,the potential collapse location of strata is derivable in accordance with a static model,the durability of roof strata can be estimated,a dynamic time step control strategy is achieved to balance the accuracy and speed of computing,and the initial crack size of rock can be estimated.In addition to the above,a mechanical model of underground excavation with non-uniformly distributed loads and partially yielded foundation is presented as the prototypical case.A set of case studies is carried out that showcase a power correlation between applied stress and roof durability.The allowable applied tensile stress for a 100-year life cycle is about 76%of the tensile strength.By using the proposed subcritical crack growth computation scheme,the roof stability in an underground excavation can be identified not only from the spatial view but also from the temporal perspective.展开更多
Subcritical crack growth of double torsion specimens made of marble was studied using Instron1342 type electro hydraulic servo test machine. The relations of the mode-I stress intensity factor KI versus the subcritica...Subcritical crack growth of double torsion specimens made of marble was studied using Instron1342 type electro hydraulic servo test machine. The relations of the mode-I stress intensity factor KI versus the subcritical crack growth velocity V and the fracture toughness KIC were obtained by the double torsion constant displacement load relaxation method. The behavior of subcritical crack growth was analyzed. The results show that lgKI-lgV relations of marble measured by this method accord with linear rule, i.e. the relations between subcritical crack growth velocity V and stress intensity factor KI have a power law, which is in good agreement with Charles theory. The testing results provide a basis for time-dependency of rock engineering stability.展开更多
To explore the formation process and mechanism of organic matter and organic-mineral complex under humification and mineralization conditions, a series of samples including humic acid, kaolin, and humic acid-kaolin co...To explore the formation process and mechanism of organic matter and organic-mineral complex under humification and mineralization conditions, a series of samples including humic acid, kaolin, and humic acid-kaolin complex were prepared using a subcritical water treatment method（SWT） under specific temperature, pressure and reaction time conditions. HA was used as a surrogate for natural organic matter because it has a similar abundant pore structure,variety of carbon types, and chemical components. These samples were used in carbamazepine（CBZ） sorption experiments and characterized by a variety of techniques. The polymerization of humic acid under the conditions of increased temperature and pressure resulted in an increase in specific surface area and molecular quantity. In addition, the degree of aromaticity rose from59.52% to 70.90%. These changes were consistent with the transformation from ‘soft carbon＇ to‘hard carbon＇ that occurs in nature. The results of sorption experiments confirmed the interaction between humic acid and kaolin from the difference between the predicted and actual Qevalues. The conceptual model of humic acid-kaolin complex could be deduced and described as follows. Firstly, the aromatic components of humic acid preferentially combine with kaolin through the intercalation effect, which protects them from the treatment effects.Next, the free carboxyl groups and small aliphatic components of humic acid interact on the surface of kaolin, and these soft species transform into dense carbon through cyclization and polymerization. As a result, humic acid-kaolin complex with a mineral core and dense outer carbonaceous patches were formed.展开更多
Effect of quenching process on the microstrucmre and mechanical properties of a kind of seamless tubes of steel 28CrMnMoV was investigated. Then, an investigation on the influence of two different quenching processes ...Effect of quenching process on the microstrucmre and mechanical properties of a kind of seamless tubes of steel 28CrMnMoV was investigated. Then, an investigation on the influence of two different quenching processes on the ductile-brittle transition behavior of this steel was undertaken. The ductile-brittle transition temperatures of the steel by two different quenching processes were also determined. The results show that a good combination of mechanical properties can be obtained through austenitizing experimental steel at 800 ℃ or 890 ℃ followed by tempering at 630 ℃. Ductile-to-brittle transition temperature of 28CrMnMoV steel austenitized at 800 ℃ followed by tempering at 640 ℃ is about -73 ℃, which is much lower than the value -37 ℃ when the steel was austenitized at 890℃ and then tempered at 650 ℃. This indicates that subcritical quenching process could decrease largely the ductile-to-brittle transition temperature of 28CrMnMoV steel.展开更多
The study of accelerator-driven subcritical reactor systems(ADSs) has been an important research topic in the field of nuclear energy for years. The main code applied in ADS research is MCNPX, which was developed by L...The study of accelerator-driven subcritical reactor systems(ADSs) has been an important research topic in the field of nuclear energy for years. The main code applied in ADS research is MCNPX, which was developed by Los Alamos National Laboratory. We studied the application of the open-source Monte Carlo codes FLUKA and OpenMC to a coupled ADS calculation. The FLUKA code was used to simulate the reaction of highenergy protons with the nucleus of the target material in the ADS, which produces spallation neutrons. Information on the spallation neutrons, such as their energy, position,direction, and weight, can be recorded by a user-defined routine called FLUSCW provided by FLUKA. Then, the information was stored in an external neutron source file in HDF5 format by using a conversion code, as required by the OpenMC calculation. Finally, the fixed-source calculation function of OpenMC was applied to simulate the transport of spallation neutrons and obtain the distribution of the neutron flux in the core region. In the coupled calculation, the high-energy cross-section library JENDL4.0/HE in ACE format produced by NJOY2016 was applied in the OpenMC transport simulation. The OECD–ADS benchmark problem was calculated, and the results were compared with those obtained using MCNPX. It was found that the flux calculations performed by FLUKA–OpenMC and MCNPX were in agreement, so the coupling calculation method for ADS is reasonable and feasible.展开更多
文摘Subcritical reactors(SCRs)or subcritical assemblies(SCAs)are the main infrastructure for designing power reactors.These reactors are widely used for training and research because of their high level of inherent safety.The objective of this study is to design a subcritical reactor using a pressurized water reactor(PWR)conventional fuel following two safety points.In the first approach,deeply placed SCR cores with an infinite multiplication factor(k_(∞))of less than unity were identified using the DRAGON lattice code.In the second approach,subcritical reactor cores with an effective multiplication factor(k_(eff))of less than unity were determined by coupling the cell calculations of the DRAGON lattice code and core calculations of the DONJON code.For the deeply subcritical reactor design,it was found that the reactor would remain inherently subcritical while using fuel rods with ^(235)U enrichment of up to 0.9%,regardless of the pitch of the fuel rods.In the second approach,the optimal pitches(1.3 to 2.3 cm)were determined for different fuel enrichment values from 1 to 5%.Subsequently,the k_(eff) was obtained for a fuel rod arrangement of 8×8 to 80×80,and the states in which the reactor would be subcritical were determined for different fuel enrichments at the corresponding optimal pitch.To validate the models used in the DRAGON and DONJON codes,the k_(eff) of the Isfahan Light Water Subcritical Reactor(LWSCR)was experimentally measured and compared with the results of the calculations.Finally,the effects of fuel and moderator temperature changes were investigated to ensure that the designed assemblies remained in the subcritical state at all operational temperatures.
基金financial support from the National Natural Science Foundation of China(No.52074349)China Scholarship Council(No.202206370108)the Hunan Provincial Innovation Foundation for Postgraduate(No.CX20230193).
文摘Subcritical crack growth(SCG)in fluid-rock interactions plays a crucial role in understanding crustal deformation and fracture network development.Using a double-torsion technique,the subcritical crack growth and fracture characteristics of Zhangzhou granite were investigated under fluids with different pH values.Subcritical crack growth index(SCI)was reduced in both acidic and alkaline fluids compared with the neutral environment,with reduction percentages of 9.8%e31.9%under acidic environment(pH=1-5)and 8.3%e17.5%under alkaline environment(pH=10-14),respectively.In contrast,the weakening effect of fluid pH values on critical stress intensity was less than that of SCI.Scanning electron microscopy(SEM)results showed that grain boundaries were prone to dissolution compared to the basal surface,proving that subcritical cracks preferentially propagate along the grain boundaries.Fracture toughness was insensitive to fluid pH values in the short term but sensitive to solution salinity.Considering mineral compositions and contents,a rock dissolution rate was defined,and a SCI prediction model was proposed,which was demonstrated to be capable of estimating variations in SCI under various fluid environments for different rock types and could provide valuable insights for engineering applications and environmental assessments.
基金support from the PipeChina Engineering Technology Innovation Co.,Ltd.(CLZB202301).
文摘Two experimental X80 steels with different Cr contents(0.13,0.40 wt.%)were designed to study the influence of Cr content on the microstructure transformation and properties in the coarse-grained heat-affected zone by using a Formastor-F II thermal dilatometer and to simulate the microstructure of the subcritically reheated coarse-grained heat-affected zone(SCGHAZ)by means of the Gleeble-3500 thermal simulator,along with the scanning electron microscope,transmission electron microscope,and electron backscattering diffraction test methods to characterize the microstructures at 650℃.The findings indicate that a higher Cr content can promote the formation of bainitic ferrite(BF),while the microhardness and impact toughness of SCGHAZ are improved.Granular bainite and BF dominated the microstructures formed by the two experimental steels at 650℃,respectively.For experimental steels mainly composed of BF,they have a high proportion of high-angle grain boundaries(HAGB),and the misorientation angle of HAGB is mostly greater than 55°.Moreover,the distribution of martensite-austenite(M-A)constituents in SCGHAZ altered from dense to sparse,and the form altered from elongated to island-like when the Cr concentration was changed from 0.13 to 0.40 wt.%.Consequently,by suitably increasing the concentration of Cr,it is possible to raise the density of HAGB and improve the shape of M-A constituents,allowing SCGHAZ to have a higher toughness.
文摘This study examines the nonlinear behaviors of a clamped-clamped porous pipe made of a functionally graded material(FGM)that conveys fluids and is equipped with a retaining clip,focusing on primary resonance and subcritical dynamics.The nonlinear governing equations for the FGM pipe are derived by the extended Hamilton's principle,and subsequently discretized through the application of the Galerkin method.The direct method of multi-scales is then used to solve the derived equations.A thorough analysis of various parameters,including the clip stiffness,the power-law index,the porosity,and the clip location,is conducted to gain a comprehensive understanding of the system's nonlinear dynamics.Through the analysis of the first natural frequency,the study highlights the influence of the flow velocity and the clip stiffness,while the comparisons with metallic pipes emphasize the role of FGM composition.The examination of the forced response curves reveals saddle-node bifurcations and their dependence on parameters such as the detuning parameter and the power-law index,offering valuable insights into the system's nonlinear resonant behavior.Furthermore,the frequency-response curves illustrate the hardening nonlinearities influenced by factors such as the porosity and the clip stiffness,revealing nuanced effects on the system response and resonance characteristics.This comprehensive analysis enhances the understanding of nonlinear behaviors in FGM porous pipes with a retaining clip,providing key insights for practical engineering applications in system design and optimization.
基金This research was supported by the Polish Ministry of Science and Higher Education,and in part by the PL Grid Infrastructure available at Academic Computer Center CYFRONET AGH.APC was funded by the AGH-University of Science and Technology,Cracow,Poland.
文摘High-level waste is an important safety issue in the development of nuclear power.A proposed solution is the transmutation of waste in fast reactors.The exclusion of the risk of supercriticality by using subcritical reactors is currently under development.Controlling the subcriticality level in such reactors presents difficulties.A problem is posed by the so-called space effect observed when using in reactors many neutron detectors in different locations of the core and reflector.Reactivity obtained from measure-ments,for example,by the Sjo¨strand method,differs by nonnegligible values.Numerical corrections can partially improve this situation.The use of a monoisotopic fission chamber set,designed for a given reactor,when each chamber is intended for a specific position in the system,can improve the situation.A question arises about the sensitivity of the results to reactivity changes.This issue is analyzed by computer simulation for possible fissionable and fissile nuclides for the total range of control rod insertion,changes in reactor fuel enrichment,and fuel temperature.The tested sensitivity was satisfactory at most levels from several dozen to several hundred pcm.A case study was conducted using the VENUS-F core model.
基金Supported by the National Natural Science Foundation of China （50578091） and Shanghai Leading Academic Discipline Project （T-105）.
文摘The hydrolysis technology and reaction kinetics for amino acids production from fish proteins in subcritical water reactor without catalysts were investigated in a reactor with volume of 400 ml under the conditions of reaction temperature from 180-320℃, pressure from 5-26 MPa, and time from 5-60 rain. The quality and quantity of amino acids in hydrolysate were determined by bioLiquid chromatography, and 17 kinds of amino acids were obtained. For the important 8 amino acids, the experiments were conducted to examine the effects of reaction temperature, pressure and time on amino acids yield. The optimum conditions for high yield are obtained from the experimental results. It is found that the nitrogen and carbon dioxide atmosphere should be used for leucine, isoleucine and histidine production while the air atmosphere might be used for other amino acids. The reaction time of 30 rain and the experimental temperature of 220℃, 240℃ and 260℃ were adopted for reaction kinetic research. The total yield of amino acids versus reaction time have been examined experimentally. According to these experimental data and under the condition of water excess, the macroscopic reaction kinetic equation of fish proteins hydrolysis was obtained with the hydrolysis reaction order of 1.615 and the rate constants being 0.0017, 0.0045 and 0.0097 at 220℃, 240℃ and 260℃ respectively. The activation energy is 145.1 kJ·mol^- 1.
文摘Effect of cryogenic treatment on the microstructure, hardening behavior and abrasion resistance of 14Cr2Mn2V high chromium cast iron （HCCI） subjected to subcritical treatment was investigated. The results show that cryogenic treatment after subcritical treatment can obviously improve the hardness and abrasion resistance of HCCI because abundant retained austenite is transformed into martensite and fine secondary carbides E（Fe, Cr）23 C6 ] precipitate. The amount of martensite and precipitated secondary carbide in HCCI experiencing subcritical treatment followed by cryogenic treatment was more than that experiencing the subcritical treatment followed by air cooling. When the abrasion resistance of HCCI reaches the maximum, its microstructure contains about 15 % retained austenite. Cryogenic treatment can further reduce the austenite content but the retained austenite cannot be transformed in to martensite completely.
基金Project(51374246,51474249)supported by the National Natural Science Foundation of ChinaProject(2013FJ6002)supported by the Science-Technology Project of Science-Technology Department of Hunan Province,China
文摘The subcritical crack growth and fracture toughness in peridotite, lherzolite and amphibolite were investigated with double torsion test. The results show that water-rock interaction has a significant influence on subcritical crack growth. With water-rock interaction, the crack velocity increases, while the stress intensity factor declines, which illustrates that water-rock interaction can decrease the strength of rocks and accelerate the subcritical crack growth. Based on Charlse theory and Hilling & Charlse theory, the test data were analyzed by regression and the correlation coefficients were all higher than 0.7, which shows the correlation is significant. This illustrates that both theories can explain the results of tests very well. Therefore, it is believed that the subcritical crack growth attributes to the breaking of chemical bond, which is caused by the combined effect of the tensile stress and the chemical reaction between the material at crack tip and the corrosive agent. Meanwhile, water-rock interaction has a vital effect on fracture toughness. The fracture toughness of samples under atmospheric environment is higher than that of samples immersed in water. And water-rock interaction has larger influence on fracture toughness in amphibolite than that in peridotite and lherzolite.
文摘In 2011,the Chinese Academy of Sciences launched an engineering project to develop an acceleratordriven subcritical system(ADS)for nuclear waste transmutation.The China Lead-based Reactor(CLEAR),proposed by the Institute of Nuclear Energy Safety Technology,was selected as the reference reactor for ADS development,as well as for the technology development of the Generation IV lead-cooled fast reactor.The conceptual design of CLEAR-I with 10 MW thermal power has been completed.KYLIN series lead-bismuth eutectic experimental loops have been constructed to investigate the technologies of the coolant,key components,structural materials,fuel assembly,operation,and control.In order to validate and test the key components and integrated operating technology of the lead-based reactor,the lead alloy-cooled non-nuclear reactor CLEAR-S,the lead-based zero-power nuclear reactor CLEAR-0,and the lead-based virtual reactor CLEAR-V are under realization.
基金supported by the Strategic Priority Research Program of The Chinese Academy of Sciences(No.XDA21010202)
文摘The accelerator-driven subcritical system (ADS) with a hard neutron energy spectrum was used to study transmutation of minor actinides (MAs). The aim of the study was to improve the efficiency of MA transmutation while ensuring that variations in the effective multiplication factor (keff) remained within safe margins during reactor operation. All calculations were completed using code COUPLE3.0. The subcritical reactor was operated at a thermal power level of 800 MW, and a mixture of mononitrides of MAs and plutonium (Pu) was used as fuel. Zirconium nitride (ZrN) was used as an inert matrix in the fuel elements. The initial mass composition in terms of weight percentages in the heavy metal component (IHM) was 30.6% Pu/IHM and 69.4% MA/IHM. To verify the feasibility of this MA loading scheme, variations in keff, the amplification factor of the core, maximum power density and the content of MAs and Pu were calculated over six refueling cycles. Each cycle was of 600 days duration, and therefore, there were 3600 effective full power days. Results demonstrated that the effective transmutation support ratio of MAs was approximately 28, and the ADS was able to efficiently transmute MAs. The changes in other physical parameters were also within their normal ranges.It is concluded that the proposed MA transmutation scheme for an ADS core is reasonable.
基金Project(BJJWZYJH01201911413037)supported by the Beijing Outstanding Young Scientist Program,ChinaProjects(51622404,41877257)supported by the National Natural Science Foundation of ChinaProject(2018SMHKJ-A-J-03)supported by Shaanxi Coal Group Key Project,China。
文摘Rock is more sensitive to tensile loading than compressive loading,since the tensile strength of rock is much lower than compressive strength.The fracture characteristics of rock in the tensile state are of great significance to the understanding of rock failure mechanisms.To this end,we have conducted numerical simulation researches on modeⅠcracking process of rock with varying homogeneity,using the Realistic Failure Process Analysis program.With the increase of homogeneity,cracks are concentrating to the ligament area with a decreasing number of crack bifurcations,and the main crack path is becoming smooth.Crack behaviors and mechanical properties are influenced significantly when the homogeneity index is in the range of 1.5 to 5.When the homogeneity index is greater than 30,they are not affected by rock homogeneity and the rock can be considered as essentially homogeneous.It is considered that the global and local strengths are affected by the distribution of rock mechanical properties at mesoscale,which influence the crack behaviors and mechanical characteristics.
基金The project supported by the National Natural Science Foundation of China (19972025)
文摘This paper studies the local dynamics of an SDOF system with quadratic and cubic stiffness terms,and with linear delayed velocity feedback.The analysis indicates that for a sufficiently large velocity feedback gain,the equilibrium of the system may undergo a number of stability switches with an increase of time delay,and then becomes unstable forever.At each critical value of time delay for which the system changes its stability,a generic Hopf bifurcation occurs and a periodic motion emerges in a one-sided neighbourhood of the critical time delay.The method of Fredholm alternative is applied to determine the bifurcating periodic motions and their stability.It stresses on the effect of the system parameters on the stable regions and the amplitudes of the bifurcating periodic solutions.
基金supported by the National Natural Science Foundation of China (No.31071541)
文摘Euphausia pacific is an important source of natural astaxanthin. Studies were carried out to assess the extractability of astaxanthin from E. pacific using subcritical 1, 1, 1,2-tetrafluoroethane （R134a）. To examine the effects of multiple process variables on the extraction yield, astaxanthin was extracted under various conditions of pressure （30-150bar）, temperature （303-343 K）, time （10-50rain）, flow rate （2-10gmin-1）, moisture content （5.5%-63.61%）, and particle size （0.25-0.109mm）. The results showed that the extraction yield increased with temperature, pressure, time and flow rate, but decreased with moisture content and particle size. A maximum yield of 87.74% was obtained under conditions of 100bar, 333K, and 30min with a flow rate of 6gmin-1 and a moisture content of 5.5%. The substantial astaxanthin yield obtained under low-pressure conditions demonstrates that subcritical R134a is a good alternative to CO2 for extraction of astaxanthin from E. pacific.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA03030102)
文摘An accelerator-driven subcritical system(ADS)is driven by an external spallation neutron source, which is generated from a heavy metal spallation target to maintain stable operation of the subcritical core, where the energy of the spallation neutrons can reach several hundred megaelectron volts. However, the upper neutron energy limit of nuclear cross-section databases, which are widely used in critical reactor physics calculations, is generally 20 MeV.This is not suitable for simulating the transport of highenergy spallation neutrons in the ADS. We combine the Japanese JENDL-4.0/HE high-energy evaluation database and the ADS-HE and ADS 2.0 libraries from the International Atomic Energy Agency and process all the data files for nuclides with energies greater than 20 MeV. We use the continuous pointwise cross-section program NJOY2016 to generate the ACE-formatted cross-section data library IMPC-ADS at multiple temperature points. Using the IMPC-ADS library, we calculate 10 critical benchmarks of the International Criticality Safety Benchmark Evaluation Project manual, the 14-MeV fixed-source problem of the Godiva sphere, and the neutron flux of the ADS subcritical core by MCNPX. To verify the correctness of the IMPCADS, the results were compared with those calculated using the ENDF/B-VII.0 library. The results showed thatthe IMPC-ADS is reliable in effective multiplication factor and neutron flux calculations, and it can be applied to physical analysis of the ADS subcritical reactor core.
基金supported by the Natural Science Foundation of Anhui Province(No.1808085MA10)Anhui Provincial Key R&D Program(No.202104g0102007)the National Natural Science Foundation of China(No.21805283)。
文摘The utilization of neutrons markedly affects the medical isotope yield of a subcritical system driven by an external D-T neutron source.The general methods to improve the utilization of neutrons include moderating multiplying,and reflecting neutrons,which ignores the use of neutrons that backscatter to the source direction.In this study,a stacked structure was formed by assembling the multiplier and the low-enriched uranium solution to enable the full use of neutrons that backscatter to the source direction and further improve the utilization of neutrons.A model based on SuperMC was used to evaluate the neutronics and safety behavior of the subcritical system,such as the neutron effective multiplication factor,neutron energy spectrum,medical isotope yield,and heat deposition.Based on the calculation results,when the intensity of the neutron source was 59×10^(13)n/s,the optimized design with a stacked structure could increase the yield of ^(99)Mo to182 Ci/day,which is approximately 16% higher than that obtained with a single-layer structure.The inlet H_(2)O coolant velocity of 1.0 m/s and initial temperature of 20℃ were also found to be sufficient to prevent boiling of the fuel solution.
基金China Scholarship Council(CSC)The University of Queensland for a Ph D fellowship。
文摘The long-term stability of the roof is particularly important in designing underground rock structures.To estimate the durability of roof strata in underground excavation,a computation scheme of subcritical crack growth is proposed in this study.By adopting the proposed method,the potential collapse location of strata is derivable in accordance with a static model,the durability of roof strata can be estimated,a dynamic time step control strategy is achieved to balance the accuracy and speed of computing,and the initial crack size of rock can be estimated.In addition to the above,a mechanical model of underground excavation with non-uniformly distributed loads and partially yielded foundation is presented as the prototypical case.A set of case studies is carried out that showcase a power correlation between applied stress and roof durability.The allowable applied tensile stress for a 100-year life cycle is about 76%of the tensile strength.By using the proposed subcritical crack growth computation scheme,the roof stability in an underground excavation can be identified not only from the spatial view but also from the temporal perspective.
基金Supported by the National Nature Science Foundation of China(50274074, 50490274) Innovation Research Project for PhD Candidate of CSU(030608)
文摘Subcritical crack growth of double torsion specimens made of marble was studied using Instron1342 type electro hydraulic servo test machine. The relations of the mode-I stress intensity factor KI versus the subcritical crack growth velocity V and the fracture toughness KIC were obtained by the double torsion constant displacement load relaxation method. The behavior of subcritical crack growth was analyzed. The results show that lgKI-lgV relations of marble measured by this method accord with linear rule, i.e. the relations between subcritical crack growth velocity V and stress intensity factor KI have a power law, which is in good agreement with Charles theory. The testing results provide a basis for time-dependency of rock engineering stability.
基金supported by the Fundamental Research Funds for the Outstanding Teachers in the Central Universities(No.35832015023)
文摘To explore the formation process and mechanism of organic matter and organic-mineral complex under humification and mineralization conditions, a series of samples including humic acid, kaolin, and humic acid-kaolin complex were prepared using a subcritical water treatment method（SWT） under specific temperature, pressure and reaction time conditions. HA was used as a surrogate for natural organic matter because it has a similar abundant pore structure,variety of carbon types, and chemical components. These samples were used in carbamazepine（CBZ） sorption experiments and characterized by a variety of techniques. The polymerization of humic acid under the conditions of increased temperature and pressure resulted in an increase in specific surface area and molecular quantity. In addition, the degree of aromaticity rose from59.52% to 70.90%. These changes were consistent with the transformation from ‘soft carbon＇ to‘hard carbon＇ that occurs in nature. The results of sorption experiments confirmed the interaction between humic acid and kaolin from the difference between the predicted and actual Qevalues. The conceptual model of humic acid-kaolin complex could be deduced and described as follows. Firstly, the aromatic components of humic acid preferentially combine with kaolin through the intercalation effect, which protects them from the treatment effects.Next, the free carboxyl groups and small aliphatic components of humic acid interact on the surface of kaolin, and these soft species transform into dense carbon through cyclization and polymerization. As a result, humic acid-kaolin complex with a mineral core and dense outer carbonaceous patches were formed.
基金Project(2008FJ1003)supported by the Hunan Province Science and Technology,China
文摘Effect of quenching process on the microstrucmre and mechanical properties of a kind of seamless tubes of steel 28CrMnMoV was investigated. Then, an investigation on the influence of two different quenching processes on the ductile-brittle transition behavior of this steel was undertaken. The ductile-brittle transition temperatures of the steel by two different quenching processes were also determined. The results show that a good combination of mechanical properties can be obtained through austenitizing experimental steel at 800 ℃ or 890 ℃ followed by tempering at 630 ℃. Ductile-to-brittle transition temperature of 28CrMnMoV steel austenitized at 800 ℃ followed by tempering at 640 ℃ is about -73 ℃, which is much lower than the value -37 ℃ when the steel was austenitized at 890℃ and then tempered at 650 ℃. This indicates that subcritical quenching process could decrease largely the ductile-to-brittle transition temperature of 28CrMnMoV steel.
基金supported by the ‘‘Strategic Priority Research Program’’ of the Chinese Academy of Sciences(No.XDA03030102)
文摘The study of accelerator-driven subcritical reactor systems(ADSs) has been an important research topic in the field of nuclear energy for years. The main code applied in ADS research is MCNPX, which was developed by Los Alamos National Laboratory. We studied the application of the open-source Monte Carlo codes FLUKA and OpenMC to a coupled ADS calculation. The FLUKA code was used to simulate the reaction of highenergy protons with the nucleus of the target material in the ADS, which produces spallation neutrons. Information on the spallation neutrons, such as their energy, position,direction, and weight, can be recorded by a user-defined routine called FLUSCW provided by FLUKA. Then, the information was stored in an external neutron source file in HDF5 format by using a conversion code, as required by the OpenMC calculation. Finally, the fixed-source calculation function of OpenMC was applied to simulate the transport of spallation neutrons and obtain the distribution of the neutron flux in the core region. In the coupled calculation, the high-energy cross-section library JENDL4.0/HE in ACE format produced by NJOY2016 was applied in the OpenMC transport simulation. The OECD–ADS benchmark problem was calculated, and the results were compared with those obtained using MCNPX. It was found that the flux calculations performed by FLUKA–OpenMC and MCNPX were in agreement, so the coupling calculation method for ADS is reasonable and feasible.
